Haemophilus ducreyi, the etiologic agent of the genital ulcer disease chancroid. H. ducreyi makes a lipooligosaccharide (LOS) that chemically and immunologically resembles human glycosphingolipid antigens. LOS may also help the bacteria adhere to and invade human cells by binding to receptors for glycosphingolipids and sialic acid. The purpose of this study is to test the hypothesis that a heptosyl transferase deficient mutant of H. ducreyi, which makes truncated LOS, is impaired in its ability to infect human skin when compared to its isogenic parent. To test this hypothesis, we will compare the ability of H. ducreyi strain 35000HP and its isogenic heptosyl transferase mutant to cause experimental infection in human subjects in dose response studies. The studies will directly test whether LOS plays a role in the ability of H. ducreyi to cause skin ulcer.